Feasibility of x-ray acoustic computed tomography as a relative and in vivo dosimeter in radiotherapy applications

by Susannah Hickling

Institution: McGill University
Department: Medical Physics Unit
Degree: MS
Year: 2015
Keywords: Physics - Radiation
Record ID: 2058309
Full text PDF: http://digitool.library.mcgill.ca/thesisfile130671.pdf


Radiotherapy is an important cancer treatment modality that uses ionizing radiation to deliver a sufficient amount of energy to kill tumour cells. Many dosimetry procedures are employed to ensure that patients receive the prescribed dose of radiation. X-ray acoustic computed tomography (XACT) is a novel imaging modality capable of producing an image of the dose distribution in a sample after irradiation by an ionizing photon or electron beam. This is achieved by exploiting the phenomenon that acoustic waves with amplitude proportional to the dose deposited are induced following a radiation pulse, and can be detected with ultrasound transducers. The goal of this work is to assess the feasibility of utilizing XACT as a dosimeter in several clinically relevant relative and in vivo radiotherapy applications. An end-to-end simulation workflow to model XACT was developed using Geant4 Monte Carlo simulations, clinical treatment planning software, and k-Wave, a MATLAB based toolkit that simulates acoustic wave propagation. To evaluate this simulation workflow, the acoustic waves induced following the irradiation of a lead rod suspended in a water tank were simulated and experimentally measured. It was found that the simulations were able to accurately determine acoustic wave properties, such as the frequency and relative amplitude trends. Additionally, the correct prediction of the peak frequency of the induced acoustic waves allowed for the development of a band-pass filter that significantly improved experimental detection by mitigating background noise.The simulation workflow was used to assess the ability of XACT to act as a tool for relative dosimetry through the simulated measurement of percent depth dose curves and in-plane profiles. The feasibility of using XACT as an in vivo dosimeter was also investigated by simulating clinical cases of prostate and breast cancer irradiation. It was found that the linear relationship between peak acoustic pressure and dose enables the measurement of percent depth dose curves with XACT. The accuracy of the simulated reconstructed in-plane profiles and clinical prostate and breast dose distributions demonstrates the capability of XACT as a tool for radiotherapy imaging. Additionally, the simulated amplitude and frequency of the induced acoustic waves indicate that they should be detectable with existing ultrasound transducer technology.This work demonstrates that XACT is a feasible dosimetry technique for a variety of relative and in vivo situations. Due to its real-time, non-invasive nature and potential to combine with ultrasound imaging, the future of XACT in radiotherapy is promising. La radiothérapie est une modalité majeure de traitement du cancer, qui utilise les rayonnements ionisants pour délivrer une quantité suffisante d'énergie pour tuer les cellules tumorales. Plusieurs procédures de dosimétrie sont employées pour s'assurer que les patients reçoivent la dose prescrite. La tomodensitométrie acoustique par rayons X (XACT) est une nouvelle modalité d'imagerie capable de…